1. Field of the Invention
The present invention relates to an image sensor, and more particularly to an image sensor which may render light entering a micro lens to have a vertical direction irrespective of the position of which portion of an external lens the light is transmitted through, by additionally disposing, at an upper portion of a micro lens array, a light-incidence regulating layer for compensating a refractive index deflection between the micro lens array and the atmosphere between the micro lens array and an external lens.
2. Description of the Prior Art
Recently, with a rapid development of the electric/electronic technologies, various electronics, such as video cameras, digital still cameras, minicam adapted personal computers (PC), minicam adapted mobile phones and so forth, employing image sensor technologies have been widely developed and used.
Traditionally, in a conventional image sensor as described above, a charge coupled device (CCD) has been generally used. However, such CCD has drawbacks in high driving voltage, a separate additional support circuit, and high per-unit prices, so that the usage thereof has been on the decrease presently.
Recently, as an image sensor for overcoming the disadvantages of the CCD, attention is attracted to a Complementary Metal Oxide Semiconductor (CMOS) image sensor. Since the CMOS image sensor is manufactured based on CMOS circuit technologies, it, contrary to the existing CCD, has advantages in that it can be driven with low voltage, it does not require an additional support circuit, it has a low per-unit price and so on.
As shown in FIG. 1, such conventional image sensor, for example, CMOS image sensor, includes a micro lens array 7 for focusing light entering from an external lens 100, a color filter array 6 for coloring light focused by the micro lens array 7, and a light-transmission layer 4 for transmitting light colored by the color filter array 6 to a photo diode array 3, which is formed in an active region of a semiconductor substrate 1 and defined by an element isolating layer 2, for generating and accumulating photocharges through receiving light transmitted through the light-transmission layer 4. On the light-transmission layer 4, a flattened layer 5 inducing a constant light transmission by planarizing a lower part of the color filter array 6 is additionally disposed.
In such image sensor system according to the prior art, as described above, light transmitted through the external lens 100 is transmitted to the photo diode array 3 through the micro lens array 7, the color filter array 6, the light-transmission layer 4, etc. Herein, light transmitted through the external lens 100 shows different incidence features to the micro lens array 7, due to a characteristic property of the external lens 100, and depending on which portion of external lens 100 the light is transmitted through.
For example, as shown in FIG. 2, light transmitted through a center portion of the external lens 100 shows an incidence feature that it is directed vertically at the corresponding micro lens 7b (i.e., the micro lens at a center portion of the semiconductor substrate), whereas light transmitted through a circumference of the external lens 100 slants to the corresponding micro lens 7a, 7c (i.e., the micro lens positioned near the circumference of the semiconductor substrate).
Herein, since the refractive index difference between the respective micro lenses 7a and 7c and the atmosphere facing the respective micro lenses is large, if light L1 or L3 incident upon the respective micro lenses 7a or 7c directly slants to the micro lenses without a separate intermediate medium, the respective micro lenses may refract corresponding light L1 or L3 at a large refraction angle and transmit the refracted light to the respective photo diodes 3a or 3c (i.e., the photo diode positioned near the circumference of the semiconductor substrate) corresponding to the respective micro lenses.
In contrast, the micro lens 7b positioned at a center portion of the semiconductor substrate 1 receives light transmitted through the external lens 100 in a direction substantially vertical to the micro lens 7b, so that the micro lens 7b can transmit corresponding light to the photo diode 3b (i.e., the photo diode positioned at the center portion of the semiconductor) without refraction.
As described above, when light slanting to the photo diode 3a or 3c positioned near the circumference of the semiconductor substrate 1 is refracted, corresponding light is unnecessarily dispersed, so that the photo diodes 3a and 3c near the circumference of the semiconductor substrate 1 receive a lesser amount of light, compared with the photo diode 3b at the center portion of the semiconductor substrate 1. That is, in the conventional system, the amount of light received by the photo diode 3a or 3c near the circumference of the semiconductor substrate is greatly different from that received by the photo diode 3b at the center portion of the semiconductor substrate unless a separate measure is adopted
In such a case that light receiving quantity is different according to the positions of the photo diodes 3a, 3b and 3c, if a separate measure is not adopted, a quantity of photocharges generated and accumulated by the respective photo diodes 3a, 3b and 3c is inconstant, with the result that presentation quality of the image is greatly degraded.
In the prior art, considering these problems, as shown in the drawing, there has been suggested a method which increases probability for light-receiving at the corresponding photo diodes 3a and 3c and thus compensates for an unbalance of light-receiving quantity in the respective photo diodes 3a, 3b and 3c, by increasing the sizes W1 and W3 of the photo diodes 3a and 3c near the circumference of the semiconductor substrate 1 relative to a size W2 of the photo diode 3b at the center portion of the semiconductor substrate 1.
However, since the difference of a concentration factor between the respective photo diodes 3a, 3b and 3c basically exists although the sizes of the photo diodes 3a and 3c are increased relative to that of the photo diode 3b, it is difficult to resolve a problem of unbalance of light-receiving in the photo diodes 3a, 3b and 3c only by regulating the sizes of the photo diodes. Further, in order to regulate the sizes of the respective photo diodes 3a, 3b and 3c differently, a complicated cell design must be performed and the overall production efficiency is greatly reduced.